Teletypewriter switchboard service observing circuit



Jan. 6, 1942. H. 6. PAGE HAL 2,269,346

TELETYPEWRITER SWITCHBOARD SERVICE QBSERVING CIRCUIT Filed Sept. 18, 1940 2 Sheets-Sheet l HEP/16E WVENTORS R. LR/CHARD ATTORNEY Jan. 6, 1942.

H. F. PAGE El AL TELETYPEWRITER SWITCHBOARD SERVICE OBSERVING CIRCUIT Filed Sept. 18, 1940 2 Sheets-Sheet 2 TU Tm HEP/16E Z RLR/CHARD II II V I tSSw mi 16: wt

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. hauqnw 28 Patented Jan. 6, 1942 TELETYPEWRITER SWITCHBOARD SERVICE OBSERVING cmcurr Harold Frederick Page, Chicago, 111., and Robert Louis Richard, Minneapolis, Minn., assignors to American Telephone and Telegraph Company,

a corporation of New York- 7 Application September 18, 1940, Serial No. 357,232

8 Claims.

This invention relates to tel'etypewriter switching circuits and more particularly to a service observing circuit for use ina teletypewriter switching system for observing service at a teletypewriter switchboard in connections involving teletypewriter cord circuits connected to tele- I typewriter subscribers line circuits or telegraph toll line circuits. H

An object of this invention is to'improve service observing circuits for use in teletypewriter switchboard service. i

A further object of this invention is .to improve service observing circuits for use in observing service involving manual cord circuits at a teletypewriter switchboard by providing a circuit which may be flexibly connected into a multiple jack of a subscribers line circuit or a multiple jack of a telegraph toll line circuit to reproduce telegraph communication signals and the supervisory signals appearing in a cord circuit connected to either .the subscribers line circuit or,

the telegraph toll line circuit.

There are anumber of different types of service observing circuits available for use in connection with teletypewriter switchboard circuits for observing service on manual connections through a teletypewriter switchboard. In certain of the circuits, telegraph communicationsignals alone are reproduced. In others .for use in connections involving a cord circuit with a subscribers line circuit, it is possible to reproduce the cord circuit supervisory signals in the observing circuit Subscribers cord circuits are used in interconnecting subscribers line circuits directly and also in connecting subscribers line circuits to telegraph toll line circuits- So far as applicants are aware, no service observing circuit is as yet available which may be flexibly intercon- The upper portion of Fig. 2 shows the observing circuit per Fig. I cooperating with a station line circuit to which a cord circuit has been connected at a teletypewriter switchboard. The lower portionof Fig. 2 vshows the observing circuit per Fig. 1 cooperating with a telegraph toll line circuit to which a cord circuit has been connected in a teletypewriter switchboard.

Refer now to the upper portion of Fig. 2. It shows a subscribers station circuit at the right connected through a subscribers loop circuit, indicated by the dotted lines. to a portionof a well-known station line circuit at a teletypewriter central station. The station line circuit extendsthe subscriber'sv station circuit and the associated loop to a. jack circuit inthe teletypewriter switchboard. The jack circuit is indicated as being a multiple jack circuit so that the station linecircuit has a number of jacks in multiple appearing at different operators positions in the teletypewriter switchboard. A portion of a well-known cord circuit by meansof which the station line circuit may be extended. towards the called station is shown at the left, of the upper portion ,of Fig. 2. A service observing circuit which, it is to be understood, is that of Fig. 1, is shown in position to engage with one ofthe multiple jack appearances of the station line circuit. The cord circuit and the service observing circuit are shown disengaged from their associatedjjacks'. When astation line circuit is under observation, the serviceobserving circuit per Fig.

1 and the cord circuit will be connected .to the indicated jacks. When the circuits are so connected, a pathmay be traced from negative batteryv I through the top winding of relay 2, through resistance 3, overthe top loop conductor through sending contacts 4, which are normally closed when thesubScribers station circuit is condimunication signals and to reproduce cord circuit supervisory signals in the service observing circuit will be understood from the following description when read with reference to the associated drawings:

Figure 1. shows the service observing circuit of the invention herein; and

Fig. 2 shows the relationship'of the observing circuit per Fig. 1 with the. circuits with which it cooperates. I

station line circuit is extended through the ring of the cord circuit'plug l I, through the top winding. of relay I2, and the armature and left-hand or marking contact'of relay l3 to. positive battery. The plug M of the observing circuit is connected. in parallel with'the cord. circuit to one of the multiple jack appearances of the station line circuit. let us assume jack 8.

Refer now to Fig. 1. The ring of plug l4 extends through the high resistance l5 to ground and also to the grids of tubes It; and I! which are connected in parallel. Battery 1 (Fig. 2) is 48 volts negative. Battery l8 (Fig. 2) is 48 volts positive. Battery [9 (Fig. 2) is 48 volts negative. The resistance I5 is 500,000 ohms, which is very high with relation to the total resistance of the various components of the station line circuit and the cord circuit.

When the sending contacts of the subscribers station are closed and the path connecting the subscribers line station with the cord circuit, which has just been traced, is completed through the armature and marking contact of relay l3, with the observing circuit connected to jack 8, a potential of approximately 42 volts negative is impressed between the ring of plug I4 and ground. When the sending contacts 4 at the subscriber's station are opened for the transmission of a spacing signal, negative battery I is disconnected from the circuit. Positive battery I8 is impressed, through a relatively low resistance, on the ring of jack l and since resistance l (Fig. 1) is inordinately high, a'potential of approximately 47 /2 volts positive is impressed between the ring of plug 14 and ground. When a signal is incoming from the distant end of the connected circuit through the cord circuit, the armature of relay 13 (Fig. 2)

is operated soas'to engage its right-hand or spacing contact and negative 48-volt battery [9 is connected to both ends of thetransmitting the ring of plug 14 contact and tip of jack 24, through the filaments of tubes 16, I1 and 20, through resistance 25, the filament of tube 2|, and through the top make contact and armature of key 22 to ground, lighting the filaments of the four tubes in series.

Battery 23 is a LS-volt battery. As indicated, its positive terminal is connected to the righthand terminal of vacuum tube 16. The resistance of the various elements in the filament circuit just traced are such that the negative side of the filaments of the various tubes are at the following potential: Tube I6 is at positive 46 volts; tube 11 is at positive 42 volts; tube is at positive 38 volts; and tube 2| is at ground potential. A circuit may be traced from battery 25 through the bottom windings of relays 28 and 21, through resistance 29 to ground. The effect of this current is to tend to operate the armatures of relays 2'! and 23 so as to engage their right-hand contacts. When the subscribers station circuit is closed and a cord circuit and a service observing circuit are connected to the multiple jacks so that approximately 42 volts positive potential is impressed between the ring of plug l4 and ground, no current will be passed through the plate circuit of tube l6, as the grid of this tube is 4 volts negative with respect to the negative side of the associated filament. Since the grid of tube I7 is of the same potential as the negative side of the associated filament, the plate circuit of tube ll will pass current. Under these circumstances, a circuit may be traced from positive battery 25 through the top winding of relay 28, through the contacts of jack 36, to the plate of tube I1, across the gap to the filament of tube 11' and to ground,

For this condition, negative 48-volt batthrough the top make contact and armature of key 22. The effect of this current preponderates over the effect of the current flowing through the bottom winding of relay 28, and the armature of relay 28 is held in engagement with its left-hand or spacing contact. A -volt battery is inserted in the plate circuit of tube 16 with its positive terminal connected to a plate and its negative terminal connected to resistance 38 which is of relatively high value, 15,000 ohms. The opposite terminal of resistance 38 is connected to the negative terminal of the filament of tube 20. Since no current flows in the output circuit of tube IS, the grid of tube 20 is at approximately the same potential as the negative terminal of its associated filament. Under these circumstances, a current will flow in the plate circuit of tube 20. This circuit may be traced from positive battery 39 through the top winding of relay 21, the contacts .of jack 40,

to the plate of tube 20, through the gap from the plate to the filament of tube 20, to ground on the top armature of key 22. The effect of this current preponderates over the effect of the current in the bottom winding of relay 21, and the armature of relay 21 is held in engagement with its left-hand contact.

When the armatures of relays 21 and 28 are held in engagement with their respective lefthand contacts, a circuit may be traced from positive battery 30, in the operators position equipment in Fig. 1, through the back contact and armature of relay 32, through resistance 33, through the Winding of the receiving magnet 34, through the bottom armature and front contact of key 22, which key is operated, through the left-hand contact and armature of relay 21, through the left-hand contact and armature of relay 28, through the top inner make contact I and armature of key 22 and through resistance 35 to negative battery. Receiving magnet 34 in the operators position equipment of Fig. 1 will therefore be energized when the subscribers station circuit is closed.

When the loop of the subscribers station circuit is opened, the potential of the grids of tubes 16 and i1 is raised, as has been shown, to positive 47.5 volts. The grid of tube I6 is now 1.5 volts positive with respect to the negative side of its associated filament. The grid of tube I1 is 5.5 volts positive with respect to the negative side of its associated filament. A current will therefore flow in the plate circuit of each of these tubes. As a result of the current flowing in the plate circuit of tube IS, the grid of tube 20, due to the large drop in resistance 38, is made exceedingly negative with respect to the negative terminal of the filament of tube 20 so that no current flows in the plate circuit of tube 20. Under these circumstances, the top Winding of relay 2'! will be deenergized and the armature of relay 2! will be actuated under the influence of current flow through its bottom winding to engage with its right-hand contact. The position of the armature of relay 28 will remain unchanged. The transfer of the armature of relay 21 from its left-hand to its right-hand contact will break the path heretofore traced through the winding of the receiving magnet in the operators position equipment in Fig. 1. The magnet will therefore be deenergized.

From the above, it should be apparent that when a marking signal is transmitted from the subscribers station a. marking signal is received in the operators position equipment in Fig. 1.

is impressed between the grids of tubes I16 and IT the distant station to which the cord circuit of Fig. 2 is connected, are reproduced in the operators position equipment of Fig. 1.

'When signals are transmitted from the distant station to which the cord circuit is connected.

the armature of relay l3 follows the signals. For the marking condition, the armature of relay I3 is in engagement with its left-hand contact -so that the potential between the ring of plug 44 and ground is the same as for a marking signal transmitted from the subscribers station. For this condition, it has been shown that the armatures of relays 21 and 28 are in engagement with their left-hand contacts and the winding of receiving magnet 34 is energized. When a spacing signal is received by relay It in the cord circuit, the armature of relay [3 is actuated to engage with its right-hand or spacing contact. Negative battery I9 is connected to one end of the subscribers loop and negative battery I is connected to the opposite end of the subscribers and ground. For this condition the grids of tubes I6 and. I1: are excessively negativel-withrespect to the negativeside" oftheir respective filaments and tubeslfi and 1'! are blocked. Tube 20, as has been shown, passes current through its plate circuit for this condition. 'As a result of the above, the'armature of relay 28 will be actuated toengage its right-hand contact. The armature of' relay 2? will remain. inengagement with its left-hand contact. A spacing signal-will be re' ceived by the magnet 34.

loop. Negative 4.8 volts approximately is impressed between the ring of plug I4 and ground. The grids of tubes [6 and I! are each approximately 48 voltsnegative with respect to ground. For this condition no current will flow in the plate circuits of tubes I5 and 11. When no current flows in the plate circuit of tube I8, it has been demonstrated that current flows in the plate circuit of tube 29. For-this-condition the armature ranged so that an operators position circuitmay g be inserted by means of a switching operation in series with the transmitting conductor of the cord circuit. The operators printer circuit may be connected in series with the transmitting conductor in either the answering or the calling end of the cord circuit as may be required. The ciriii) If the'operators printer circuit is connected in the transmitting conductor'on the opposite side of the cord circuit, the -transmission of signals from the operators-printer will result in the op-" eration of relay l3. For the marking condition, the transmitting conductor through the top winding of relay l3 will be closed. The armature of relay I3 will be held in engagement with its left-hand contact. It has been shown that this will result in the reception of a marking signal by magnet 34. When a spacing signal is transmitted from the operators printer, the path through the top windingof relay l3 will be opened and the armature'oi relay 13 will be actuated to engage with its right-hand -or spacing contact, so that negative battery will be connected to each end of the subscribers'loop. It has been shown thatfor this condition a spacing signal is received by magnet 34.

The use of a high resistance i5 connected between the grids of the tubes "Sand 11 and ground results in a definite potential being-impressed on the grids when the plug I4 is disconnected from the jack circuit. Under these circumstances, the circuit through the receiving rnagnet 34' is'maintained open, resulting inapermanent' spacing signal being received by the-associated printer. As a resultof this, the associated printer runs open which prevents the printing of random characters due to slight fluctuations in the grid potentials.

. a cord circuit.

cuit of the invention herein is arranged to func-- tion when an operators printer circuit is so connected in either end of thecord'circuit.

If the operators printer circuit isconnected in the transmitting conductor of the cord'circuit between the subscribers station circuit and the polar relays in the cord circuit, when a marking sig nal is transmitted from the operators printer, the transmitting conductor is closed. The conditions in, Fig. ,1 resulting from this are the same as obtained when a marking signal is transmitted from-the subscriber's station and a marking signal is therefore reproduced in the operators position equipment. When a spacing signal is transmitted from the operators printer circuit, the transmitting conductor is opened in the 0perators printer circuit. For this condition the batteries in the cord circuit are ineffective. Battery I, however, is connected thnough the subscribers'loop on the rings of jacks 8, 9 and I0 and the circuit is extended through the ring of plug M'through high resistance l5, which resistance is of the order of 500,000 ohms to ground. The drop between thering of plug M and ground hi DU The circuit of Fig. 1 will function also when a cord circuit is connected to a toll line circuit, as indicated in the bottom portion of Fig. l. The voltage conditions on the ring of plug 15 are practically identical with the voltage condition described for the condition when a subscribers station and station line circuit are connected to When a cord circuit is connected to a toll line circuit, positive battery is connected through the marking contact and armature of relay l3 in the cord circuit through the top wind-' ing of relay l2, through the ring of plug H,

through the ring. of the associated toll line jack 46 to'negative battery. For this condition the relative values of the resistance units in the circuit are such'that with plug [4 of Fig. 1 connected to one of the multiple jacks of the toll line circuit, the voltage impressed between the grids of tubes 16 and H and groundis approximately 42 volts positive. This is the same voltage as is impressed on-the grids of tubes 16 and I1 for the marking condition when the service observing circuit per Fig. 1 is cooperating with a connection involving a cordcircuit-and a-station line circuit andsubscribers station circuitz A a result of this; as has beenshown, a marking signal is received by magnet 34. When the armature of relay 48 in the hybrid repeater circuit is actuated so as to engage its right-hand or. spacing contact, positive battery in the hybrid repeater is connected to one end of the transmitting conductor and positive battery in the cord circuit is connected to the opposite end of the transmitting conductor. The voltage of both of these batteries is the same, namely 48 volts. Forthis condition, positive 47.5 volts approximately is impressed between the grids of tubes I6 and I1 and ground. This is the same voltage as was impressed on the grids of these tubes for a spacing signal transmitted from the subscribers station. It results in a spacing signal being received by magnet 34 in the manner which has already been described.

In the case of signals received from a distant station connected to the opposite end of the cord circuit, in a connection involving a toll line circuit, for the marking condition the armature of relay l3 will be held in engagement with it lefthand or marking contact and the voltage condition will again be the same as for a marking signal transmitted from the hybrid repeater.

When a spacing signal is received from the distant end of the circuit connected to the cord circuit, the armature of relay [3 will be actuated to engage with its right-hand or spacing contact and negative battery 19 will be connected to one end of the transmitting conductor and negative battery will be connected to the marking contact of relay 46. For this condition, approximately 48 volts negative potential will be impressed between the grids of tubes I8 and I1 and ground. As

a result of this condition, a spacing signal will be received in magnet 34.

The circuit herein is arranged to indicate that a particular subscribers station line circuit to which it may be connected is in the open condition, which is the normal conditon when the loop through the subscribers station is not in use. Under such circumstances, no cord circuit will be connected to any of the multiple jacks associated with the station line circuit. When .2

the subscribers loop throughthe subscribers station is not in use, it is openand there will be no battery connected to the ring of any of the jacks. Consequently, as described above, there will be no current flowing in the output circuits of tubes 15 and H. For this condition the circuit through the receiving magnet in the operators position equipment will be opened which will cause the receiving teletypewriter to run open in a manner well known in the art. This will indicate that an idle line has been selected.

When a subscribers station is in the idle condition before his loop is closed to establish a direct current path, as is well known in the art, the subscribers loop is closed through a condenser not shown which shunts the contacts of the station switch to permit the station to be rung. When an open station line circuit is rung by machine ringing from the calling end of the cord circuit, the monitoring set runs open, thus giving an indication that the subscriber is being rung. When ringing is sent manually from the answering end of the cord, the monitoring set runs open during the ringing interval.

The manner in which the circuit of the invention herein functions to reproduce disconnect and flashing recall signals will now be described. A circuit may be traced from negative battery 58 in the cord circuit through the winding of relay 51 and the back contact and armature of relay 58 to the tip of plug H. When plug H is inserted into one of the multiple jacks associated with a station line circuit, the circuit is extended through the tip of the jack, through the winding of relay 59 to the front contact of relay 60. The station line circuit shown in Fig. 2 is not shown in complete detail as it is well known in the art. When the subscribers station circuit and its associated station line circuit is connected through a cord circuit and is conditioned for communication, relay 89 is unoperated so that the circuit last traced is open at the front contact and armature of relay 60. When a disconnect signal is sent from the subscribers station circuit, relay 68 is operated in a manner well known in the art so as to connect ground through the armature of relay 58 to the circuit last traced. When the observing circuit per Fig. 1 is connected to one of the multiple jacks, such as jack 8, and a ground indicating a disconnect signal is impressed from the armature of relay 68 through the tip of jack 8 and the tip of plug 14, it is extended to the grid of tube 2|. The negative side of the filament of tube 2] is at ground potential. A current will, therefore, flow in the circuit which may be traced from battery 41 through the Winding of relay 48, the contacts of jack 46 to the plate of tube 2|, across the gap between the plate and the filament of tube 2| to ground connected to the make contact and armature of key 22. This will operate relay 48. The operation of relay 48 will, in turn, operate relay 49 over an obvious circuit. The operation of relay 48 will, in turn, operate relay 58 over an obvious circuit. When relay 50 operates, it will lock up from ground through the contacts of key 5| and the right-hand armature and front contact of relay 50, through the winding of relay 50 to battery. The operation of relay 49 also closes the circuit from ground through the left-hand front contact and armature of relay 49 and the left-hand armature and front contact of relay 50, through the filament of lamp 52 to battery, lighting lamp 52. When lamp 52 is lighted steadily in response to a steady ground connected through the armature of relay 60, it indicates a disconnect signal.

For a flashing recall signal, relay 60 is momentarily operated and released in a Well-known manner. In response to this, relay 48 is energized to light lamp 52 and thereafter relay 48 is released, in turn releasing relay 49. Relay 50 remains operated since it has been looked as described. The release of relay 49 connects ground through the interrupter 55 and the lefthand back contact and armature of relay 49, through the left-hand armature and front contact of relay 58 and the filament of lamp 52 to battery, causing lamp 52 to flash, as an indication that a flashing recall signal is being transmitted from the subscribers station.

If the armature of relay 21 or 28 is actuated so as to engage with its respective right-hand contact and remains in engagement with its right-hand contact for a protracted interval, relay 53, which is a slow-to-operate relay, will be operated. The circuit which is established when the armature of relay 28 is actuated so as to engage with its right-hand contact may be traced from battery through resistance 35 and the top inner armature and front contact of key 22, through the armature and right-hand contact of relay 28 and the winding of relay 53 to ground. If the armatureof relay 28 remains in engagement with its left-hand contact and the armature of relay 2'! is actuated so as to engage with its right-hand contact, the circuit for the operthrough resistance 35, through the top inner armature and front contact of key 22, through the armature and left-hand contact of relay 28, through the armature and right-hand contact of relay 2'! and through the winding of relay 53 to ground. When, after an interval, relay 53 operates, lamp 54 is lighted over an obvious circuit. At the same time a circuit is closed from battery 30 through the break contact and armature of relay 32, through resistance 33, through the winding of the receiving magnet in the operators position equipment, through the bottom armature and front contact of key 22 and through the left-hand front contact and armature of relay 53 to ground. This energizes the receiving magnet 34 and prevents the teletypewriter machine in the operators position equipment from running open.

The function of jack 24 is to permit the measurement of the filament current in tubes [6, H, and 2|. The function of jacks 36, 40 and 46 is to permit the measurement of the plate current in each of the tubes with which each jack is associated.

What is claimed is:

1. In a teletypewriter switching system, a teletypewriter cord circuit, a teletypewriter subscribers line and station circuit, means for interconnecting said circuits at a first time, a teletypewriter toll line circuit, means for interconnecting said cord circuit to said toll line circuit at a second time, a teletypewriter service observing circuit, means for interconnecting said. service observing circuit at said first time to said connection comprising said cord circuit and said subscribers line and station circuit, means for interconnecting said observing circuit at said second time to said connection comprising said cord circuit and said toll line circuit, and means in said circuits for reproducing communication signals and supervisory signals transmitted through said connected circuits in said observing circuit.

2. In a teletypewriter switching system, a teletypewriter cord circuit, a subscribers teletypewriter line and station circuit, a telegraph toll line circuit, means for connecting said cord circuit at a first time to said subscribers line and station circuit to form an operable telegraph path, means for connecting said cord circuit at a second time to said toll circuit to form a second operable telegraph path, means for transmitting communication signals and supervisory signals over each of said paths, a teletypewriter service observing circuit, means for connecting said service observing circuit to either of said paths, and means for reproducing said communication signals and said supervisory signals transmitted over either of said paths in said observing circuit when so connected.

3. In a teletypewriter switching system, a telegraph service observing circuit, means in said observing circuit for connecting said circuit to a telegraph path including a switching device at a manual teletypewriter switchboard, an electron discharge device in said observing circuit responsive to changes in potential in said path, due to supervisory signals, and means also in said observing circuit, responsive to said discharge device, for reproducing supervisory signals transmitted over said path.

4. In a teletypewriter switching system, a telegraph signal path, means for transmitting telegraph communication signals thereover, means for transmitting supervisory signals thereover, a telegraph service observing circuit, means in said circuits for flexibly interconnecting said circuits so that service over said path may be observed, means including a first electron discharge devicein said observing circuit for reproducing communication signals transmitted over said path and means including a second electron discharge device in said observing circuit for reproducing supervisory signals transmitted over ond polar relay in said circuit responsive to control means in a telegraph circuit to which said observing circuit is connectable, and a series circuit extending through thewinding of a telegraph signal receiving device and through armatures and contacts on each of said relays.

6. In a teletypewriter switching system, a telegraph service observing circuit, three electron discharge devices, three relays each having a winding in series with the output of said devices and means responsive to said relays, for reproducing communication and supervisory signals in said observing circuit.

7. In a teletypewriter switching system, a service observing circuit, a conductor in said observing circuit connectable to an operable telegraph path including a switching device in a teletypewriter switchboard, a first and a second electron discharge device in said observing circuit, a grid in each of said devices connected in parallel to said conductor so as ,to impress substantially uniform potentials between said grids and ground, a common series circuit extending through a filament in each of said devices, and means for controlling said devices so that the output circuit of one of said devices conducts current while at the same time the output circuit of the other of said devices is substantially blocked.

8. In a teletypewriter switching system, a service observing circuit connectable toan operable telegraph path including a manual switching cord circuit, a first, second and third electron 1 "I-IAROLD FREDERICK PAGE. ROBERT LOUIS RICHARD. 

